1. Field of the Invention
The present invention is directed generally to methods and devices for treating conditions, such as strabismus, in which a patient is unable to achieve reliable binocular fixation.
2. Description of the Related Art
The retina is a light-sensitive tissue lining the inner surface of an eye. The retina converts light to nerve impulses that are transmitted by the optic nerve to the visual cortex of the brain. Vision is the result of the brain's interpretation of these nerve impulses.
Binocular disparity refers to small differences in portions of a scene captured by each eye resulting from each eye viewing the same scene from a slightly different position. These differences make stereoscopic or binocular vision possible. Binocular vision (also referred to as stereopsis) incorporates images from two eyes simultaneously. In other words, the two images are fused together into a single stereoscopic image. The slight differences between the two images seen from slightly different positions make it possible to perceive distances between objects in what is commonly referred to as depth perception.
Binocular vision occurs when both eyes operate together without diplopia, suppression, or visual confusion. Diplopia is the perception of two images of a single object. Binocular diplopia refers to double vision in which images of an object are formed on non-corresponding points on the retinas of the eyes. Suppression is the inability to perceive an image or part of an image from one eye when both eyes are open. Visual confusion is the perception of two objects (one imaged by each eye) at the same location.
Strabismus is a disorder in which the eyes do not line up in the same direction during binocular fixation. In other words, the eyes are looking in different directions instead of fixating on (foveating) a single point. Strabismus can result in double vision (diplopia), visual confusion, uncoordinated eye movements, vision loss in one eye, and a loss of the ability to see in three dimensions also known as a loss of depth perception. Children with strabismus may learn to ignore visual input from one eye (referred to as suppression). If this continues long enough, the eye that the brain ignores may experience a loss of vision referred as amblyopia. Amblyopia is sometimes referred to as “lazy eye.”
Orthoptics is the evaluation and nonsurgical treatment of visual disorders caused by improper coordination of the eye muscles, such as strabismus. Binocular vision therapy is another term that can be used as synonymous with orthoptics. Orthoptic devices have been developed to treat strabismus and amblyopia. For example, a prism may be used to bend light to produce a properly aligned image on the retinas of the eyes that the brain could fuse into a stereoscopic image. Similarly, an amblyoscope is an instrument (a reflecting stereoscope) configured to stimulate vision in an amblyopic or lazy eye. An amblyoscope may also be used to measure or train binocular vision. A synoptophore is a type of amblyoscope. A haploscope presents one image to one eye and another image to the other eye and may be used to treat strabismus and amblyopia.
As a practical matter, the terms haploscopes, amblyoscopes, and synoptophores are largely synonymous with one another. There are two primary methods used clinically with these devices. First, the devices are used to provide temporal co-stimulation of a large-field (about 15 degrees of the visual field in diameter). Second, the devices are used to attempt or achieve perceptual fusion of dichoptic displays (displays that are different in each of the two eyes). An example of a dichoptic display is a pair of images, one of a deer and the other of spots. The deer display is shown to one eye and the spots display to the other eye. The brain creates a fused image of a deer with spots on it.
Unfortunately, these conventional approaches provide diffuse and spatially uncertain stimulation to a patient's eyes. Therefore, a need exists for a device configured to provide more precise and/or spatially certain visual stimulation to a patient's eyes. Further, a need exists for other methods and devices for treating strabismus and/or other conditions in which a patient is unable to achieve reliable binocular fixation and thus may not have sufficiently reliable binocular vision. The present application provides these and other advantages as will be apparent from the following detailed description and accompanying figures.